The Tempest, as Anne Barton once pointed out, is an obliging work of art. It can be seen, among myriad other things, as anti-colonialist tract, theatrical metaphor and spiritual allegory. And Trevor Nunn, in this new production, leans very much towards the last.

It's a deeply traditional production, with none of the startling innovations of a Rupert Goold, but one that coherently and satisfyingly treats the play as a parable about the triumph of virtue over vengeance.

It occasionally runs the risk of sentimentality. The final passages of reconciliation are swathed in soothing, mock-baroque music. Giles Terera's Caliban, having been dispossessed of his island kingdom, rather tamely submits to Prospero's patronising beneficence at the conclusion. And the final handshake between Prospero and his usurping brother exceeds the bonds of fraternal love: Antonio, after all, is the man who kicked Prospero out of Milan, incites Sebastian to an act of regicide, and remains ominously silent at the play's end. All that makes his supposed climactic conversion a little too good to be true.

But, although Nunn's production softens some of the play's harsher edges, it boasts in Ralph Fiennes a Prospero full of the right tortured nobility. Fiennes is particularly good in the opening passages. He quietly mutters spells as he assumes his magic mantle. He looks totally exhausted by the effort of summoning up the sea storm. And he illumines every stage of his long recital of his past history, showing especial tenderness to Miranda as he reassures her "a cherubin thou wast that didst preserve me".

This offers an early clue to Fiennes's performance. Beneath the testiness and the hunger for vengeance lurks an essentially gentle, bookish spirit; and this pays off handsomely at the end when he places a loving hand on Ariel's shoulder to release him from captivity.

Other actors may have shown us more of Prospero's darker side. John Wood gave us a Freudian wreck battling with his own internal demons. Michael Bryant was a nut-brown necromancer who looked as if he may genuinely have commanded graves to open. And Patrick Stewart was an Arctic solitary with Faustian delusions. But Fiennes brings to the role a strong sense of Prospero's anguished virtue and speaks the verse excellently. "Our revels now are ended" becomes not a glowing cosmic recital but a particularised vision of the fragility of mortal things.

Three other performances stand out. Tom Byam Shaw's Ariel is an airborne spirit who belies his diaphanous otherness by positively shaking with fervour when he makes his plea for "liberty". Andrew Jarvis also lends the old counsellor, Gonzalo, a sense of mature wisdom not least in his vision of a commerce-free Utopia. And Chris Andrew Mellon invests the crown-hungry Sebastian with a glittering malignancy.

I was also mildy amused by Clive Wood and Nicholas Lyndhurst who turn Stephano and Trinculo into a re-run of the Toby Belch-Andrew Aguecheek relationship from Twelfth Night.

It's also a production that, in Stephen Brimson Lewis's design and Paul Pyant's lighting, looks handsome: the appearance of the three goddesses is particularly well done as a piece of neo-Handelian opera with Juno seen standing on top of a fan-decorated bridge. It's not a Tempest that offers any startling revelations or insights in the manner of the Peter Brook, Jonathan Miller or Giorgio Strehler versions, but it boasts a strong performance from Fiennes, adorns the Haymarket Theatre and, like the vision conjured up by Prospero, is "harmonious charmingly".